BEIJING  China's southern Guangdong province scrambled to protect its water supplies on Thursday as a toxic waste spill from a zinc smelter flowed along a major river towards several sprawling cities, state media reported.

It is the second environmental disaster to hit the country in as many months after an explosion at a chemical plant in the northeast poisoned drinking water for millions and sent a frozen, poisonous slick heading slowly but surely towards Russia.

Cadmium levels had been found to be 10 times normal in the Shaoguan city section of the North River cutting across Guangdong province north to south after the smelter's discharge of waste during an equipment maintainence last week.

Several villages and factories near Yingde, a city 90 km (54 miles) downstream from Shaoguan, had been without running water for days, Xinhua news agency said on Thursday.

At a suburban Yingde cement plant, fire engines had been dispensing drinking water to thousands of workers and their families, Xinhua said.

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"Taps are only on for showers in the evening for a couple of hours. We've been collecting drinking water with plastic buckets from fire engines since Sunday," a worker surnamed Lu told Reuters by telephone.

The city has shifted to a nearby reservoir to draw drinking water for its 100,000 residents, Xinhua said.

Cadmium, a metallic element widely used in batteries, can cause liver and kidney damage and lead to bone diseases. Compounds containing cadmium are also carcinogenic.

STALL AND DILUTE

The most-polluted stretch of water has arrived at Shakou township, 30 km upstream from Yingde, and dam gates at the nearby Baishiyao hydropower plant had been lowered to stall it, a local government spokesman told Reuters by telephone.

"We want to dilute the toxins there by reservoirs further upstream increasing discharges and then flush them quickly past Yingde," the spokesman, surnamed Wang, said. "But we are still waiting for the experts to decide when to do that."

The diluted pollutants should not affect Foshan and the provincial capital, Guangzhou, cities of 800,000 and 9 million in the booming Pearl River Delta manufacturing hub, Xinhua said.

"Nevertheless, the two cities have been asked to start emergency plans to ensure safe drinking water," Xinhua news agency said.

Qingyuan city, between Guangzhou and Yingde and with a population of half a million, has also launched emergency measures.

In Shaoguan, authorities had halted operations at the zinc smelter -- China's third largest -- and shut down another 14 small smelters, Xinhua said.

In China's northeast, the Songhua River toxic slick was expected to reach the Russian border city of Khabarovsk on Thursday but workers dammed a waterway to divert the pollution away from Khabarovsk's water supplies, Xinhua said in a separate report.

"With the dam, the toxic slick will steer clear of Khabarovsk's water intake in the lower reaches of the Fuyuan waterway, ensuring the water safety in the city," Xinhua quoted Meng Wei, head of the Chinese Research Academy of Environmental Science, as saying.